Influence of nitrogen, phosphorus, and potassium fertilization on the mineral concentrations of medicago sativa L. II. Diurnal and day to day fluctuations

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Abstract
An established stand of alfalfa was fertilized with different combinations of N, P and K. The rate used per nutrient was constant for all combinations. The study was conducted to evaluate the effect of fertilizer application, diurnal change and period to period fluctuation on the mineral composition of alfalfa. Two experiments were conducted at different stages of morphological maturity. Experiment one (E‐1) was initiated when regrowth after an initial hay harvest was in the late‐vegetative to early‐bud stage. The second experiment (E‐2) was initiated when regrowth from E‐1 was approximately 20 cm tall. Phosphorus application significantly increased the P concentrations in alfalfa, but decreased the Cu levels in both experiments. Potassium applications significantly decreased the levels of Ca, Mg, Na, Cu, Zn, Mo and Co. Levels of all minerals analyzed in E‐1 were significantly different from period to period while only seven of the sixteen were significantly changed in E‐2. Period to period differences were partially explained by rainfall pattern. Significant diurnal variations were found for K, Ca, Mn, B, Sr, and Zn in E‐1 and for Ca, SiO2, and Sr in E‐2. The N, P, and K applied and the P and K available in the soil were correlated with cation levels in alfalfa and the interrelationships were discussed.